Oligonucleotides have been used in various biological and biochemical applications. They have been used as primers and probes for the polymerase chain reaction (PCR), as antisense agents used in target validation, drug discovery and development, as ribozymes, as aptamers, and as general stimulators of the immune system. As the popularity of oligonucleotides has increased, the need for producing greater sized batches, and greater numbers of small-sized batches, has increased at pace. Additionally, there has been an increasing emphasis on reducing the costs of oligonucleotide synthesis, and on improving the purity and increasing the yield of oligonucleotide products.
A number of innovations have been introduced to the art of oligonucleotide synthesis. Amongst these innovations have been the development of excellent orthogonal protecting groups, activators, reagents, and synthetic conditions. The oligonucleotides themselves have been subject to a variety of modifications and improvements. Amongst these are chemistries that improve the affinity of an oligonucleotide for a specific target, that improve the stability of an oligonucleotide in vivo, that enhance the pharmacokinetic (PK) and toxicological (Tox) properties of an oligonucleotide, etc. These novel chemistries generally involve a chemical modification to one or more of the constituent parts of the oligonucleotide.
The term “oligonucleotide” thus embraces a class of compounds that include naturally-occurring, as well as modified, oligonucleotides. Both naturally-occurring and modified oligonucleotides have proven useful in a variety of settings, and both may be made by similar processes, with appropriate modifications made to account for the specific modifications adopted. A naturally occurring oligonucleotide, i.e. a short strand of DNA or RNA may be envisioned as being a member of the following generic formulas, denominated oligo-RNA and oligo-DNA, respectively, below: